The invention relates generally to lightning protection systems, and more specifically to a lightning protection system for wind turbine blades and aircraft wings (airfoils).
A wide variety of lightning protection systems for protection of wind turbines and their associated blades are known within the art. Wind turbines are usually erected in open spaces or in more recent years at sea where they form the highest point and often attract lightning. The tips of the wind turbine blades reach the highest position and are therefore the usual place of impact for lightning.
In the past, the fact that blades were often made of a non-conductive material such as glass fibre lead to the belief that lightning was not a problem. However, such blades are often covered by a thin layer of dust, salt or pollution and together with moisture, the risk of conducting a current is real and results in several unprotected blades being damaged or destroyed by lightning. Recent discoveries have demonstrated that the geometry of rotor blades also plays a determinant role in the lightning arc formation and discharge process.
The issue of establishing lightning protection for wind turbine blades has generated several different solutions. One solution is intended to prevent the electrical current from a lightning striking the blades of the wind turbine from entering the generator and other electrical and electronic components situated in the top or in the nacelle of the wind turbine. This is done by conducting the electrical current from the blades to the tower of the wind turbine and to the ground or earthing system.
Based on their height and exposed positions, wind turbines offer preferred impact positions for lightning strikes. Wind turbine installations in regions with high ceraunic activities especially require sophisticated protection systems. Most endangered components are the electrical installations, the control electronics and the blades. Later ones are manufactured of glass-fiber or carbon-fiber reinforced plastics. Their damage or destruction due to lightning results in the longest down-time of the facility.
Modern wind turbines are equipped with blades of approximately 37 m length and above. Although being made of electrically insulating glass-fiber reinforced plastics, the blades form preferred impact spots for a lightning discharge. To avoid damage or destruction by lightning strikes, these blades are equipped with a lightning protection system (LPS). The most common LPS consists of several metallic discrete receptors that are implemented into the blade shell and that are internally connected to ground by a down-conductor. The receptors provide defined impact positions for the lightning strike. A lightning electric discharge is expected to commute on the external part of the rotor blade from one receptor to the other in order to reduce the formation of electric discharges and arcs inside the rotor blade. For shorter blades, this concept proved to be sufficient, but for longer blades, some portions of the blade surface continue to be unprotected.
State-of-the-art wind turbine blade lightning protection systems used various forms of discrete external receptors, which are distributed along the rotor blade surface to attract a lightning flash. Due to the limited number of receptors, there is a high probability that lightning strikes hit the blade between two receptors, leading to partial to total destruction of the composite material.
Due to this problem, alternative lightning protection systems have been proposed. One system includes the lamination of a metallic lattice, conductive and flexible foils onto the outer blade shell. The processing step of including a metallic lattice into the lamination procedure however, makes later ones more complicated and can also increase the costs due to the higher material expenses.
In similar fashion, state-of-the-art lightning protection systems for aircraft wings (airfoils) make use of various forms of integration of a conductive path on the surface, e.g. a mesh, especially for composite material based wings, with the disadvantage that partial and local damage can be caused by the lightning attachment point. The area close to the lightning attachment point for an airfoil can usually be damaged, which in some cases requires additional repairs after landing or at least an inspection. This situation can result in more downtime of the aircraft and thus increases the operational costs and reduces the availability of the aircraft.
In view of the foregoing, it would be advantageous to provide a lightning protection system for wind turbine blades and aircraft wings (airfoils) that avoids the foregoing problems and expenses.